Automotive and non-automotive body panels etc. are commonly manufactured using hot-forming techniques, in which heated sheet-metal blanks are made to conform to the shape of a cavity that is formed between the surfaces of forming tools that are mounted in a press. Superplastic forming is a specific example of a hot-forming process for forming sheet metal articles. It works upon the principle of superplasticity, which means that a material can elongate beyond 100% of its original size under carefully controlled conditions. An advantage of the superplastic forming process is that large and complex articles can be formed in a single operation, thereby reducing the need to assemble together smaller components while at the same time achieving weight reduction. Further, the formed article has excellent precision and a fine surface finish.
Exterior body panels of automobiles, the so-called “Class A surfaces,” provide styling and aesthetic qualities that are intended to appeal to prospective buyers of an automobile. In general, “Class A surfaces” can be regarded as any surface that has styling intent. It is therefore common to form exterior automotive body panels with curves and contours, which give the finished automobile a sleek and “sexy” appearance. In the increasingly competitive automotive industry, a consumer's first impression in a dealer showroom can make all the difference in a sale.
Normally, the design of shaped articles including automotive body panels is such that the forming tool that is used to form the article will have forming tool walls that extend at a positive draft angle, and thereby ensure ease of removal of the finished article from the forming tool. However, in some instances the desired shape of the finished article requires that the forming tool have a negative draft angle by undercutting a wall of the forming tool cavity. Unfortunately, in such instances the finished article is locked within the forming tool and cannot be removed. Of course, various solutions have been proposed for enabling the removal, from a tool, of formed articles having a negative draft angle.
In United States Patent Application Publication 2005/0150266 Kruger et al. disclose a forming tool system including a finish-form tool that advances and retracts in accordance with a curvilinear path. The finish-form tool is pivotably mounted about a fixed pivot axis, such that the finish-form tool may separate from the formed article in accordance with the negative draft angle. Unfortunately, the entire finish-form tool pivots about the fixed pivot axis and therefore the extent to which the finished article may be undercut is limited. In particular, a deeply undercut section necessitates movement of the finish-form tool along a curvilinear path having a large radius, which path may be obstructed by other portions of the finished article.
In U.S. Pat. No. 7,306,451 Kruger et al. disclose a forming tool apparatus for forming an article, including a first forming tool having a removable cavity wall segment with an undercut cavity wall. A pivot linkage normally establishes the removable wall segment in a forming position in which the undercut wall is poised for forming of the article. The pivot linkage selectively pivots the removable wall segment out of the forming position when the forming tools are opened, so that the undercut wall is pivotally lifted and releases the formed article for removal from the cavity. Unfortunately, this system is very complex and relies on a pivoting movement of the removable wall segment to unlock the formed article. This requires the pivoting of a very large and heavy portion of the tool, which is designed such that the removable wall segment encompasses the entire Class A region of the article, and which results in other issues relating to making the necessary electrical connections, wire flexing fatigue, etc. As a result, implementing this system tends to be cost prohibitive.
It would be beneficial to provide a process and forming tool apparatus that overcome at least some of the above-mentioned limitations and disadvantages of the prior art.